The present invention relates to a roller for rewinding and tensioning a flexible element, with greater length than width, for example a flexible sheet of material or a shutter or rolling shutter with jointed elements. The invention applies in particular, but without thereby restricting the scope of the disclosure, to the field of industrial protections, to the manufacture of rolling screens or guards (for example, those used to isolate machine tools) or to protect and guard certain machine parts such as slideways. Protections of this kind have flexible elements which roll up onto rollers and which can be unrolled to prevent machine parts not only from knocking against extraneous objects or coming into contact with shavings or swarf but also from being dirtied by contact with acids or pollutants in general. Similar protection devices may also be used as movable covers, strong enough to be walked on, if necessary, placed over the installation pits of large machines or as rolling covers for tanks.
A roller of the type described above is the object of U.S. Pat. No. 5,775,619, issued to the Applicant, the disclosure of which is hereby incorporated by reference.
Similar rollers substantially consist of a tubular body, sealed at the ends by two flanges which are axially drilled to allow the passage of the ends of a support shaft which lies coaxial to the roller. One end of the flexible element is fixed to the external surface of the tubular body.
The flanges and the shaft are connected in such a way that they can turn, and can rotate relative to one another about a shared axis. Moreover, the tubular body and shaft are rigidly fixed to opposite ends of a helical wire spring, which is housed inside the tubular body. The connection at the ends of the spring is made using support and connecting parts which have the shape of a cylindrical pad, inserted axially into the spring and screwed onto the coils at the end sections of the spring, by means of surfaces with suitable matching grooves. The connecting parts are then rigidly fixed, one to the shaft, and the other to the tubular body. When the flexible element is pulled, so as to unroll it from the roller, the spring or springs are subjected to a torsion which causes elastic energy to accumulate in the springs. The said energy is then returned in the form of a force couple which, forcing the roller to rotate in the opposite direction, allow the rewinding and relative tensioning of the flexible element about the tubular body.
A specific problem with such rollers is related to the fact that, in most applications, the length of the flexible elements is usually much greater than the width.
As a result, the rollers have relatively small axial dimensions and, when used, are subjected to a high number of rotations about their axes in order to wind and unwind the flexible element. This means that the axial length of the springs used for this purpose is considerable, so that the said springs are often too long to be housed in the tubular body.
A solution to this problem which allows a compromise between the overall dimensions of the roller and the generation of elastic forces of suitable intensity for rewinding the flexible element, was obtained by fitting two or more springs, positioned coaxial to one another, inside the tubular body. However, this solution, which proved satisfactory in some applications, remained problematic in other cases. In fact, it must be noticed that when the flexible element is unwound, for each turn of the roller relative to the shaft, a length of wire substantially corresponding to the length of a coil is unwound from the spring, so that the axial dimension of the spring increases by one coil. As a result, for each turn of the roller relative to the shaft, with equal torque applied to the spring, the diameter of the spring is reduced and the spring contracts towards the axis of the shaft. Therefore, when fitting the spring or springs to the roller, it is necessary to fix the ends of the springs at a distance greater than the largest axial dimension that they occupy when wound down, so as to ensure that the coils are separated by a given distance.
The gap created between one coil and the next must be such that, when the spring is loaded, following unwinding of the flexible element from the roller, the spring can extend freely and, at its maximum load, reach a compact configuration in which all of the coils make contact with one another. During the assembly stage, it is, therefore, necessary to consider the presumable number of turns envisaged for each roller, then fit the springs with the coils spaced sufficiently.
The afore-mentioned assembly method has several disadvantages, mainly due to the fact that during rotation of the roller relative to the shaft and the consequent loading of the spring, the latter takes on an irregular shape about its own axis, shifting from one place to another inside the roller and hitting against the internal surface of the roller. This leads to the creation of points of wear on the spring which are not uniform and an abnormal deformation of its wire.
Moreover, the afore-mentioned configuration, especially where two or more springs are fitted coaxially, implicates the possibility of the coils of two springs interfering with one another or becoming entwined. The aim of the present invention is to eliminate the afore-mentioned technical disadvantages.